Some good news in Earth Security

Looks like we may not be in as much danger as we thought.

NEOWISE observations indicate that there are at least 40 percent fewer near-Earth asteroids in total that are larger than 330 feet, or 100 meters. Our solar system's four inner planets are shown in green, and our sun is in the center. Each red dot represents one asteroid. Object sizes are not to scale. Image credit: NASA/JPL-Caltech

In 1998, Congress asked NASA to map the skies and determine just how many asteroids that could wreck havoc--from Armageddon to "Downtown is now a crater--news at 11."  This means asteroids roughly 330 meters in size and spanning as far as the asteroid belt.  the result id good news for the Earth...and not-so good news for Hollywood or Armageddon alarmists.  The estimate of asteroids that could destroy our home has been cut significantly:  from 35,000 to about 19,500.

The main reason:  we can judge sizes better in infrared, which is what NASA is using in its Wide-field Infrared Survey Explorer.  Using infrafre rather than visible light, we can get a better idea of the size of an object because it doesn't depend on how well the object reflects light.  A material's ability to reflect light is it's albedo.  As you can see from this image, a small object with a high albedo looks as bright as a big object with a low albedo.  In infrared, however, the size is more apparent.
So the number of wreck-your-world asteroids is cut.  Does that help us?  Perhaps, in that we can more easily track them.  Of the large asteroids, 981 have been found, and we're tracking 911 already, for example.

Of course, the real question is, should we see one heading our way, what can we do?  At least we know the chances of that happening are smaller.  None of the large planet-killers should be heading our way for a few centuries, according to NASA, so we have some breathing time.

Full article here:

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